In a vehicular air conditioner including an air mix damper that adjusts a flow rate of air delivering to a heater core through an evaporator and a flow rate of air bypassing the heater core through the evaporator, the temperature is adjusted by rotating the air mix damper at an appropriate position between the maximum cooling position (MAX COOL position) and the maximum heating position (MAX HOT position). In such an air-mix type vehicular air conditioner, the pressure loss of air flow paths is larger at the heating side than the cooling side. The opening degree needs to be adjusted precisely for controlling the temperature around the maximum heating position.
It is known that when the air mix damper is slightly opened to a slight opening degree from the maximum heating position for controlling the temperature, air is delivered into a gap provided by the slight opening having a high aspect ratio, and accordingly, a stable vortex street is generated. Due to the vortex street, dissonant high-frequency sounds (commonly known as whistling) are generated. Since the high-frequency sounds are transmitted to a cabin with temperature-conditioned air through a blowing port, a feeling of unpleasantness is given to occupants. Thus, for minutely controlling the flow rate while preventing the occurrence of the high-frequency sounds when the air mix damper is slightly opened, it is proposed that a plurality of asperities are formed on the distal end of the air mix damper. It is also proposed that a pair of seal lips for closing a gap between the air mix damper and a seal surface of a unit case are provided and asperities are formed on the distal ends of the seal lips (for example, see Patent Literatures 1 to 3).